The present invention relates to a concept for allocating geographical position measurement values to geographical maps or objects of such maps, as can be used, for example, for improving the accuracy of such position measurement values.
When determining measurement values for respective geographical positions interval by interval while driving or walking through roads or paths, more or less great inaccuracies result, depending on the method used. The currently most widespread navigation system is the global positioning system (GPS). Since artificial signal distortion was abandoned several years ago, locating accuracies of 10 to 15 meters can be obtained with little effort. Thereby, the locating accuracy depends also on the number of satellites that are “seen” at the measurement time. Generally, it can be said that the measurement accuracy increases with the number of received satellites.
If, however, one is moving in an urban area with partly highly built-up roads or narrow alleys, it can happen that buildings shade a line of sight to satellites, and hence the measurement accuracy achievable by GPS decreases. If geographical raw data measured by a satellite position determination system are placed into geographical town maps or maps, relatively implausible location indications can result that have only little in common with the actual geographical position of the navigation device. This applies in particular for narrow alleys and footpaths where even an accuracy of 10 to 15 meters can result in implausible results. In particular at crossroads it can be difficult to decide which road an inaccurately measured point is to be allocated to.
Thus, frequently, geographic raw data measured by navigation systems are matched to map data, so that, for example, a driver receives plausible position information on the display of the navigation device his vehicle. If the accuracy of the position determination is currently at approx. 50 meters, for example, and if a driver is moving along a road at the side of a lake, it would be very confusing if the position of the vehicle on the display of the navigation device were not indicated on the road but in the lake—even if the raw measurement values provide a (wrong) position in the lake. In such cases, a navigation system detects that such a position is extremely unlikely for applications in a road navigation system and corrects the measured geographical position for display in the geographical map such that the same corresponds to a plausible position, for example on a road.
Due to the increasing distribution of wireless radio networks, for example based on the WLAN standard (Wireless Local Area Network), these wireless networks offer themselves as a basis for new localization methods. In WLAN-based locating systems, frequently a so-called received signal strength (RSS) fingerprinting is used as a basic method. This method is based on the assumption that the signal strengths of radio signals of several radio stations received or receivable at a current location unambiguously characterize the current location or the current geographical position. If a reference database exists which contains, for a number of geographical reference locations or reference positions, the transmitter identifications of radio stations received or receivable there at reference times, as well as the signal strengths of the corresponding radio signals, the current position can be inferred from a set of current measurement values (transmitter identifications and associated signal strength values) by matching the currently measured measurement values and the reference values of the database. This matching evaluates for every reference point how similar its previously recorded measurement values or reference values are to the current measurement values of the current position. The most similar reference point(s) is/are used as a basis for an estimated value for the current position of the mobile terminal device.
From this, it is obvious that the accuracy of such WLAN-based localization systems depends among others on the quality of the reference positions in the reference database. The signal strength of a radio transmitter receivable at a reference position at a reference measurement time is determined experimentally for a reference database by a reference measurement. This results in a database containing a list of radio transmitters (access points) including the respective associated received field strength and quality for every reference position where a reference measurement has been performed. Thereby, the reference positions are determined, for example, by GPS devices. The accuracy of such measurements has already been discussed above.